Present soils and past land use: the “bracken economy” in Lea-Artibai County (Basque Country, northern Spain) in the late nineteenth and early twentieth centuries

Soils in Lea-Artibai County (northern Spain) show three significant features: frequent absence of A horizons, higher nutrient concentrations in the surface mineral horizon of past or present arable fields compared to those in forest or shrubland, and the common presence of calcareous horizons in arable fields which is out of character with the region’s humid climate. Farmers stopped applying lime around 1950, so the third feature is interpreted as the result of over-liming since the eighteenth century. The “maize revolution” that began in the mid-seventeenth century relied upon a three-crop rotation system using bracken as a primary fertilizer along with animal manure and lime obtained from local kilns that burned gorse. Extraction of these plant materials resulted in a negative phosphorus balance of phosphorus and the acidification of shrubland soils. The county could not accommodate these various land uses in the early twentieth century, and extraction of leaf litter from forests and shrublands became necessary. In the “concentrational agriculture” of the maize revolution, organic matter and nutrients accumulated in arable fields and diverted ecological pressure onto shrubland and forest soils, creating a “metabolic rift” that is still evident in the soils of Lea-Artibai County.